Heretofore, methods of spraying a quick-setting concrete in which a powder quick-setting admixture was admixed with a concrete, were applied to prevent break and fall of ground exposed in excavation works of tunnels or the like (cf. JP-B-60-004149 and JP-A-09-019910).
These spraying methods employed a quick-setting admixture in which an alkali metal aluminate, an alkali metal carbonate or the like was admixed with calcium aluminate because of its excellent quick-setting property.
However, there has been an increasing demand for a quick-setting admixture having a pH-value lower than that of the quick-setting admixture in which an alkali metal aluminate, an alkali metal carbonate or the like was admixed with calcium aluminate, and being weakly alkaline, preferably neutral or weakly acidic.
Liquid quick-setting admixtures proposed for this purpose include one composed mainly of a basic aluminum salt and an organic carboxylic acid (cf. JP-A-2001-509124), one composed mainly of aluminum sulfate and an alkanolamine (cf. JP-A-10-087358) and one composed mainly of a basic aqueous solution of aluminum, lithium silicate, and lithium aluminate (cf. JP-A-2001-130935).
However, these liquid quick-setting admixtures had problems that it is hard to achieve satisfactory initial strength development and that it is not easy to realize heavy-spraying in a tunnel, as compared with the conventional powder-type quick-setting admixtures.
Furthermore, quick-setting admixtures containing fluorine in addition to aluminum sulfate were developed as acidic liquid quick-setting admixtures with an increased quick-setting property (cf. JP-A-2002-080250, JP-A-2002-047048 and JP-A-2004-035387).
However, there were desires for further improvement in the quick-setting property, improvement in the adherability in a spring place, and so on for practical use. In addition, expectations were recently high for development of a liquid quick-setting admixture having less effect on the human body and better initial strength development than those of the conventional basic quick-setting admixtures.